The present invention relates to an apparatus for forming a radial tire mounted on a passenger car or the like.
Methods forming a radial tire are broadly divided into two methods.
A first method is a method in which when an inner liner and a ply which constitute a carcass layer serving as a back cloth are assembled into a carcass band, the outer peripheral length thereof is larger than the outer peripheral length of a bead core, and the bead core is installed by decreasing the diameters (usually, referred to as ply down) of a bead core region and a bead core outside portion. A second method is a method in which the outer peripheral length of a carcass band, which is same as described above, is smaller than the inner peripheral length of the bead core, and the bead core is installed by increasing the diameter (usually, referred to as bead lock) of the bead core region.
The present invention relates to an improvement in the latter second method.
Further, the second tire forming method is classified into three methods (method A, method B1, and method B2). Of these three methods, method A is a method in which xe2x80x9cafter the bead core is installed on the carcass band, a portion between the bead cores are swelled into a toroidal shape, and then the carcass band (including a sidewall) in the outside end portion of both of the bead cores is folded and pressed so that the bead core is wrapped in the aforementioned toroidal carcass bandxe2x80x9d, and a ring-shaped belt-tread structure, which is assembled in advance to the toroidal outer peripheral portion, is assembled, by which a green tire for radial tire is completed. This method is a forming method in which xe2x80x9cthe carcass band including the sidewall is foldedxe2x80x9d.
Method B is a method in which xe2x80x9cafter the bead core is installed on the carcass band, a portion between the bead cores is slightly expanded into a cylindrical shape, and then the carcass band in the outside end portion of both of the bead cores is folded and pressed so that the bead core is wrapped in the aforementioned cylindrical carcass bandxe2x80x9d, and a ring-shaped belt tread structure, which is assembled in advance, is assembled to the outer peripheral portion swelled into a toroidal shape, by which a green tire for radial tire is completed. Of method B, method B1 is a tire forming method in which the carcass band including the sidewall is folded, and method B2 is a tire forming method in which the carcass band not including the sidewall is folded and subsequently the sidewall is affixed.
In all of the above-described three methods, a tire construction called a tread over sidewall, in which the end portion of tread is provided so as to cover the outside of the end portion of sidewall, is used to improve the productivity.
In the case of such a construction, if the position in which the sidewall end is affixed is inexact relative to the end position of belt layer, the durability and quality of tire is seriously affected.
In the conventional forming machine of method A,
(I) A rubber bag called a bladder is used for folding, and careful attention is paid to the performance and quality control of bladder and the operation control of equipment for the above-described reasons. However, great swelling occurs from a portion near the bead diameter of tire to a position near the outside diameter of tire, and the dimensions inevitably change with use. Therefore, it is difficult to make the degree of swell of right and left bladders uniform and to stabilize the slip of bladder surface.
(II) Further, taking notice of the behavior near the end of pressing of the member end portion (explanation is given in a portion at the left of the equator line of toroidal tire), there is a problem in that a member on the bladder having a curvature that is convex toward the right flies to the toroidal carcass having a curvature that is convex toward the left while rolling on the curvature while sliding on the bladder by means of the shrinkage force of member, by which the affixing position is made unstable.
Contrarily, in method B1, a single bladder is used for folding, and the amount of swell in the radial direction is regulated by the action of a rollover ring, so that the amount of swell is remarkably small. Therefore, the profile after the bladder has swelled is stable. Further, because of the folding action in which transfer is effected in the state in which the member is held between the bladder and the ring inside cylinder face, the profile is stable as compared with method A.
Contrarily, in method B2, after the folding work, the end portion of sidewall can be affixed with a projected bright line representing the affixing position to be controlled being the reference, the sidewall end portion on the tire equator line side has a high accuracy as compared with method B1.
The bladder used for folding is classified into a single bladder type and a dual bladder type. The single bladder type is a type in which one bladder is used on one side of a forming drum. The dual bladder type is a type in which two bladders are used. For the single bladder type, in order to assist the folding action of the swelled bladder, a ring-shaped body called a xe2x80x9cpush canxe2x80x9d or a xe2x80x9crollover ringxe2x80x9d is indispensable.
For the folding in method B2, any of a rollover type using the single bladder, a push can type using the single bladder, and a dual bladder type can be used. The type to be used is determined by the length of folding and the construction and arrangement of forming equipment.
For the purpose of the improvement in high-speed durability, a tire having a two-layer construction of plies constituting the carcass has been needed.
As the two-layer construction, the following types have been considered. (Herein, a ply bonded to an inner liner layer in the cross section of a completed tire is called a first ply.)
(a) A type in which the two-layer construction is formed by laminating a ply with the same width as that of the first ply on the first ply so as to be slightly shifted in the axial direction of a forming former. In this case, the position of ply end folded while wrapping the bead core is almost the same as that of the tire of one-layer construction, and lies close to the bead core of sidewall.
(b) A type in which the two-layer construction is formed by laminating a ply with a width slightly narrower than that of the first ply on the first ply. In this case, the position of ply end is similar to that in item (a).
(c) A type in which the overall two-layer construction is formed by one ply by increasing the width of the first ply and by lapping the folded plies on each other at the tire equator position.
(d) A type in which the overall two-layer construction is formed by making the width of the first ply equal or approximately equal to the width of tire of one-layer construction and by adding a second ply extending to both end portions of the folded first ply.
(e) A type in which the substantial two-layer construction is formed by one ply by increasing the width of the first ply and by positioning the end portion of the folded ply slightly on the tire equator position side of the end portion of the belt layer.
(f) A type in which the two-layer construction is formed by making the width of the first ply equal or approximately equal to the width of tire of one-layer construction, by adding the second ply to the end portion of the first ply, and by positioning the end portion of the second ply slightly on the tire equator position side of the end portion of the belt layer.
When a tire of two-layer construction of each of these types is to be produced, in method A,
The two-layer construction of items (a) and (b) can be formed.
The two-layer construction of item (c) cannot be formed because of a too large length of folding.
The two-layer construction of item (d) can be formed if the construction is such that the folded first ply is lapped on the second ply, but cannot be formed if the construction is such that the second ply is lapped over the folded first ply.
The two-layer construction of items (e) and (f) can be formed, but has a problem described below.
Since the folding length is large, the swell of bladder must be increased as compared with the above-described cases (I) and (II), and further there is added a new problem in that since the folded ply end is longer than the sidewall end, when the member flies to the toroidal carcass as described in case (II), the end portion of ply only has a higher shrinkage speed than the lamination region of sidewall and ply, so that there arises a problem in that the affixing position becomes more unstable.
In method B, for the push can type and dual bladder type, of the above-described constructions, only the constructions of items (a) and (b) can be formed. In methods B1 and B2 using the rollover ring, the constructions of items (a) to (f) can be formed without being affected by the folding length.
As forming equipment of method B, forming equipment disclosed in Japanese Patent Publication No. 53-24463 is publicly known, but this forming equipment has the following problems.
(1) According to this invention, xe2x80x9ca step of forming a cylindrical tire band to which a bead member is assembled on a tire forming drum and a step of folding both end portions of the tire band around the bead member after the diameter of the drum is increased and then affixing a tire sidewall constructing member to form a green casexe2x80x9d are implemented on the same drum. The publicly know drum capable of being used in such steps has a bladder that wraps the bead core, so that the surface thereof is not flat, which interferes with the exact winding of thin-wall inner liner and ply.
(2) As described above, the bladder used for folding is classified into the single bladder type and the dual bladder type. The single bladder type is a type in which one bladder is used on one side of the forming drum. The dual bladder type is a type in which two bladder is used.
For the single bladder type, in order to assist the folding action of the swelled bladder, the ring-shaped body called the xe2x80x9cpush canxe2x80x9d or the xe2x80x9crollover ringxe2x80x9d is indispensable. In this invention, however, consideration is not given to the action and arrangement of this ring-shaped body, so that the dual bladder type must inevitably be used.
As a result, this invention is unsuitable to the formation of a tire of a construction in which the folding length is large in folding a band at both sides of the bead core (the aforementioned items (c), (d), (e) and (f)).
The present invention has been made in view of the above situation. Accordingly, an object of the present invention is to provide a radial tire forming apparatus in which when a thin-wall inner liner and a ply are assembled, the stiffness is high, and these materials can be wound exactly and pressed firmly on a flat surface. Another object of the present invention is to provide a radial tire forming apparatus provided with a folding device that can be applied to the formation of a carcass band having a large folding length, especially, a tire constructed so that the fold end portions are lapped on each other at the tire equator position.
To achieve the above objects, the present invention provides tire forming equipment including a first forming process including a carcass band forming process in which a dedicated forming former for forming a carcass band is provided at a first forming point A, and an inner liner and a ply are laminated on the band forming former provided with a flat and stiff forming surface, by which a carcass band with an outside diameter smaller than the inside diameter of a bead core is formed; a carcass forming process including a carcass forming former with a diameter smaller than the inside diameter of carcass band and rollover work (work for folding and wrapping the bead core) at a second forming point C; and a carcass band conveying process for reciprocating the carcass band between these two processes; a second forming process in which a sidewall is wound on the carcass structure having been completed by the first forming process at a third forming point E to complete a green case; and a third forming process for assembling a belt-tread structure after the green case is made in a toroidal shape at a fourth forming point, including a green case conveying process for receiving the green case at the third forming point E and delivering it at the fourth point H; a belt-tread structure forming process for forming the belt-tread structure at a fifth forming point I; and a belt-tread structure conveying process for conveying the belt-tread structure from the fifth forming point I to the fourth forming point H. Thus, during the time when the carcass forming former 11 moves from the second forming point C to the third forming point E, the rollover work is performed.
Also, the present invention is preferably configured so that the rollover device is constructed as described below. The rollover device includes a frame moving longitudinally toward the former on guide rails disposed in parallel with the forming former axis of the carcass forming process; a driving unit for the frame; a guide shaft capable of moving longitudinally on the frame toward the former disposed in parallel with the forming former axis; a thin-wall, ring-shaped first rollover ring which is fixed at the end of the former side of the guide shaft and is disposed coaxially with the former axis; and a thin-wall, ring-shaped second rollover ring which is mounted so as to be movable on the guide axis and is disposed coaxially with the former axis, and the rollover device is constructed so that the first and second rollover rings can be moved individually and synchronously. Also, the rollover device is constructed so that the rollover device is mounted in a housing portion for supporting the former, which is constructed so that the carcass forming former reciprocates between the second forming point and the third forming point, so that the operation of rollover ring can be performed even during the movement of the carcass forming former.
Also, in the radial tire forming apparatus in accordance with the present invention, for a tire constructed so that the fold end portions of carcass band are lapped on each other, when the first rollover ring and second rollover ring are brought close to the center of the forming former, in the first half of approaching operation, the rollover rings are brought close to the forming former synchronously and are stopped once at a respective xe2x80x9cfirst advance stop positionxe2x80x9d, and in the second half of operation, either one of the rollover rings is advanced to a xe2x80x9csecond advance stop position (work finish position)xe2x80x9d, and at an appropriate time during the retreat, the other rollover ring is advanced to the xe2x80x9csecond advance stop positionxe2x80x9d of that rollover ring, by which rollover work can be performed alternately.
Further, in the radial tire forming apparatus in accordance with the present invention, the diameters of the rollover rings are different from each other so that when the first rollover ring and second rollover ring are brought closest to each other, the cylindrical portions of the rings enter and lap on each other, by which the size of the equipment of carcass forming process is decreased.